The invention relates to oils transesterified with short-chain fatty acid esters, and having improved lubrication properties.
Oils used in industrial applications are typically petroleum based hydrocarbons that can damage the environment, as well as pose health risks to people using them. Plant oils are an environmentally friendly alternative to petroleum based products, and are based on renewable natural resources. The major components of plant oils are triacylglycerols (TAGs), which contain three fatty acid chains esterified to a glycerol moiety. The polar glycerol regions and non-polar hydrocarbon regions of TAGs are thought to align at the boundaries of metal surfaces, and thus have better lubricant properties than petroleum hydrocarbons.
The low temperature properties and oxidative stability of plant oils, however, limit their use for industrial applications. Industrial oils must be liquid and have a reasonable viscosity at low temperatures. Most plant oils do not possess such low temperature properties. For example, high erucic rapeseed oil has a pour point (i.e., the temperature at which the oil ceases to flow) of xe2x88x9216xc2x0 C., but undergoes a significant increase in viscosity with decreasing temperatures.
Industrial oils also must have high oxidative stability, which generally is related to the degree of unsaturation present in the fatty acyl chains. Reaction of a plant oil with oxygen can lead to polymerization and cross-linking of the fatty acyl chains, and decreased oxidative stability. Saturated hydrocarbon based oils have no unsaturation and therefore have high oxidative stability.
The invention is based on transesterifying short saturated fatty acid esters with triacylglycerol containing oils, such as vegetable oils, to obtain oils having improved lubrication properties. Although vegetable oils are known to provide good boundary lubrication, their low oxidative stability and poor low temperature properties often prevent them from being utilized in lubrication applications. Transesterifying various short saturated fatty acid esters with a vegetable oil improves oxidative stability and low temperature properties due to the increased saturation and the heterogeneity of the fatty acids esterified to the polyols.
In one aspect, the invention features a method for improving lubrication properties of a vegetable oil. Lubrication properties can include wear properties, viscosity, or crystallization temperature. The method includes transesterifying the vegetable oil with a short chain fatty acid ester. The vegetable oil can have a monounsaturated fatty acid content of at least 50%, e.g., at least 70%, and can be selected, for example, from the group consisting of corn oil, rapeseed oil, soybean oil, and sunflower oil. Canola oil is a particularly useful rapeseed oil. The short chain fatty acid ester can be saturated, and can be from four to 10 carbons in length. In particular, the short chain fatty acid ester can be from six to 10 carbons in length. The short chain fatty acid ester can be normal or branched, and can be a methyl ester or a polyol ester, such as a neopentyl glycol ester, a pentaerythritol ester, or a trimethylolpropane ester. Trimethylolpropane triheptanoate is a useful trimethylolpropane ester.
The method further can include adding an amount of an antioxidant effective to increase oxidative stability of the transesterified vegetable oil. The antioxidant can be selected from the group consisting of hindered phenols, dithiophosphates, and sulfurized polyalkenes. The amount of antioxidant can be about 0.001% to about 10% by weight.
The invention also features an oil comprising a glycerol polyol ester and methods for making such oils. Oils of the invention further can include an antioxidant, an antiwear additive, a pour-point depressant, an antirust additive, or an antifoam additive. The glycerol polyol ester of such oils is characterized by the formula: 
wherein R1, R2, and R3 are independently aliphatic hydrocarbyl moieties having three to 23 carbon atoms, wherein at least one of R1, R2, and R3 have a saturated aliphatic hydrocarbyl moiety having three to nine carbon atoms, and wherein at least one of R1, R2, and R3 have an aliphatic hydrocarbyl moiety having 11 to 23 carbon atoms. The saturated aliphatic hydrocarbyl moiety can be, for example, a hexyl moiety, a heptyl moiety, or a nonyl moiety. The aliphatic hydrocarbyl moiety having 11 to 23 atoms can be derived from oleic acid, eicosenoic acid, or erucic acid.
Oils of the invention further can have a non-glycerol polyol ester. The non-glycerol polyol ester can be characterized by the formula: 
wherein R4 and R5 are independently aliphatic hydrocarbyl moieties having three to 23 carbon atoms, wherein at least one of R4 and R5 have a saturated aliphatic hydrocarbyl moiety having three to nine carbon atoms, and wherein at least one of R4 and R5 have an aliphatic hydrocarbyl moiety having 11 to 23 carbon atoms, wherein R6 and R7 are independently a hydrogen, an aliphatic hydrocarbyl moiety having one to four carbon atoms, or, 
wherein X is an integer of 0 to 6, and wherein R8 is an aliphatic hydrocarbyl moiety having three to 23 carbon atoms. For example, R6 can be an ethyl moiety, and R7 can be, 
wherein X is 1 and R8 is an aliphatic hydrocarbyl moiety having three to 23 carbon atoms.
In an alternative embodiment, the invention features an oil that includes a non-glycerol polyol ester. The non-glycerol polyol ester is characterized by the formula: 
wherein R1 and R2 are independently aliphatic hydrocarbyl moieties having three to 23 carbon atoms, wherein at least one of R1 and R2 have a saturated aliphatic hydrocarbyl moiety having three to nine carbon atoms, and wherein at least one of R1 and R2 have an aliphatic hydrocarbyl moiety having 11 to 23 carbon atoms, wherein R3 and R4 are independently a hydrogen, an aliphatic hydrocarbyl having one to four carbon atoms, or, 
wherein X is an integer of 0 to 6, and R5 is an aliphatic hydrocarbyl moiety having three to 23 carbon atoms.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.